Dynamic Noise Reduction in Auditory Prosthesis Systems

ABSTRACT

An exemplary method of dynamically adjusting an amount of noise reduction applied in an auditory prosthesis system includes dividing an audio signal presented to a patient into a plurality of analysis channels each containing a signal representative of a distinct frequency portion of the audio signal, determining an overall noise level of the signals within the analysis channels, and dynamically adjusting an amount of noise reduction applied to the signals within the analysis channels in accordance with the determined overall noise level. The dynamic adjustment of noise reduction is configured to minimize the amount of noise reduction applied to the signals within the analysis channels if the overall noise level is less than a predetermined minimum threshold. Corresponding methods and systems are also disclosed.

RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/241,471 by Leonid M. Litvak etal., filed on Sep. 11, 2009, and entitled “Dynamic Noise Reduction inCochlear Implant Systems,” the contents of which are hereby incorporatedby reference in their entirety.

BACKGROUND INFORMATION

The sense of hearing in human beings involves the use of hair cells inthe cochlea that convert or transduce acoustic signals into auditorynerve impulses. Hearing loss, which may be due to many different causes,is generally of two types: conductive and sensorineural. Conductivehearing loss occurs when the normal mechanical pathways for sound toreach the hair cells in the cochlea are impeded. These sound pathwaysmay be impeded, for example, by damage to the auditory ossicles.Conductive hearing loss may often be overcome through the use ofconventional hearing aids that amplify sound so that acoustic signalscan reach the hair cells within the cochlea. Some types of conductivehearing loss may also be treated by surgical procedures.

Sensorineural hearing loss, on the other hand, is caused by the absenceor destruction of the hair cells in the cochlea which are needed totransduce acoustic signals into auditory nerve impulses. People whosuffer from sensorineural hearing loss may be unable to derivesignificant benefit from conventional hearing aid systems, no matter howloud the acoustic stimulus is. This is because the mechanism fortransducing sound energy into auditory nerve impulses has been damaged.Thus, in the absence of properly functioning hair cells, auditory nerveimpulses cannot be generated directly from sounds.

To overcome sensorineural hearing loss, numerous auditory prosthesissystems (e.g., cochlear implant systems) have been developed. Auditoryprosthesis systems bypass the hair cells in the cochlea by presentingelectrical stimulation directly to the auditory nerve fibers. Directstimulation of the auditory nerve fibers leads to the perception ofsound in the brain and at least partial restoration of hearing function.

To facilitate direct stimulation of the auditory nerve fibers, a leadhaving an array of electrodes disposed thereon may be implanted in thecochlea of a patient. The electrodes form a number of stimulationchannels through which electrical stimulation pulses may be applieddirectly to auditory nerves within the cochlea. An audio signal may thenbe presented to the patient by translating the audio signal into anumber of electrical stimulation pulses and applying the stimulationpulses directly to the auditory nerve within the cochlea via one or moreof the electrodes.

Noise reduction has been shown to be beneficial to cochlear implantpatients. However, noise reduction is not always desirable. For example,in quiet environments, noise reduction may result in the patient feelingdisconnected from the environment because environmental sounds may notbe audible.

SUMMARY

An exemplary method of dynamically adjusting an amount of noisereduction applied in an auditory prosthesis system includes dividing anaudio signal presented to an auditory prosthesis patient into aplurality of analysis channels each containing a signal representativeof a distinct frequency portion of the audio signal, determining anoverall noise level of the signals within the analysis channels, anddynamically adjusting an amount of noise reduction applied to thesignals within the analysis channels in accordance with the determinedoverall noise level. The dynamic adjustment of noise reduction isconfigured to minimize the amount of noise reduction applied to thesignals within the analysis channels if the overall noise level is lessthan a predetermined minimum threshold.

Another exemplary method of dynamically adjusting an amount of noisereduction applied in an auditory prosthesis system includes dividing anaudio signal presented to an auditory prosthesis patient into aplurality of analysis channels each containing a signal representativeof a distinct frequency portion of the audio signal, determining anoverall noise level of the signals within the analysis channels,minimizing an amount of noise reduction applied to the signals withinthe analysis channels if the overall noise level is less than apredetermined minimum threshold, and progressively increasing the amountof noise reduction applied to the signals within the analysis channelsin response to a progressive increase in the overall noise level abovethe predetermined minimum threshold.

An exemplary system for dynamically adjusting an amount of noisereduction applied in an auditory prosthesis system includes a frequencyanalysis facility configured to divide an audio signal into a pluralityof analysis channels each containing a signal representative of adistinct frequency portion of the audio signal and a noise reductionfacility communicatively coupled to the channel facility. The noisereduction facility is configured to determine an overall noise level ofthe signals within the analysis channel and dynamically adjust an amountof noise reduction applied to the signals within the analysis channelsin accordance with the determined overall noise level. The dynamicadjustment of noise reduction is configured to minimize the amount ofnoise reduction applied to the signals within the analysis channels ifthe overall noise level is less than a predetermined minimum threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments and are a partof the specification. The illustrated embodiments are merely examplesand do not limit the scope of the disclosure. Throughout the drawings,identical or similar reference numbers designate identical or similarelements.

FIG. 1 illustrates an exemplary auditory prosthesis system according toprinciples described herein.

FIG. 2 illustrates a schematic structure of the human cochlea accordingto principles described herein.

FIG. 3 illustrates exemplary components of a sound processing subsystemaccording to principles described herein.

FIG. 4 illustrates exemplary components of a stimulation subsystemaccording to principles described herein.

FIG. 5 illustrates an exemplary cochlear implant system according toprinciples described herein.

FIG. 6 illustrates components of an exemplary sound processor coupled toan implantable cochlear stimulator according to principles describedherein.

FIG. 7 illustrates an exemplary dynamic noise reduction method accordingto principles described herein.

FIG. 8 shows exemplary components that may be included within a noisereduction module that may be used to determine the overall noise levelof the signals within a plurality of analysis channels according toprinciples described herein.

FIGS. 9-11 illustrate exemplary mapping functions according toprinciples described herein.

FIG. 12 illustrates another exemplary dynamic noise reduction methodaccording to principles described herein.

DETAILED DESCRIPTION

Methods and systems for dynamically adjusting an amount of noisereduction applied in an auditory prosthesis system are described herein.In some examples, an audio signal presented to an auditory prosthesispatient (e.g., a cochlear implant patient) may be divided into aplurality of analysis channels each containing a signal representativeof a distinct frequency portion of the audio signal. An overall noiselevel of the signals within the analysis channels may then bedetermined. An amount of noise reduction applied to the signals withinthe analysis channels may be dynamically adjusted in accordance with thedetermined overall noise level. As will be described in more detailbelow, the dynamic adjustment of noise reduction is configured tominimize the amount of noise reduction applied to the signals within theanalysis channels if the overall noise level is less than apredetermined minimum threshold. In this manner, a minimal amount ofnoise reduction may be applied when the patient is located within arelatively quiet environment. The amount of applied noise reduction maybe progressively increased in response to a progressive increase in theoverall noise level. Such dynamic application of noise reduction to anaudio signal may allow an auditory prosthesis patient to perceiveenvironmental sounds present within the quiet environment that wouldotherwise be rendered imperceptible with noise reduction heuristics usedin more noisy environments.

FIG. 1 illustrates an exemplary auditory prosthesis system 100. As shownin FIG. 1, auditory prosthesis system 100 may include a sound processingsubsystem 102 and a stimulation subsystem 104 configured to communicatewith one another. As will be described in more detail below, auditoryprosthesis system 100 may be configured to determine an overall noiselevel of an audio signal presented to an auditory prosthesis patient andautomatically adjust an amount of noise reduction applied to the audiosignal in accordance with the determined noise level.

Sound processing subsystem 102 may be configured to detect or sense anaudio signal and divide the audio signal into a plurality of analysischannels each containing a signal representative of a distinct frequencyportion of the audio signal. Sound processing subsystem 102 may befurther configured to determine an overall noise level of the signalswithin the analysis channels and dynamically adjust an amount of noisereduction applied to the signals within the analysis channels inaccordance with the determined overall noise level. Sound processingsubsystem 102 may then transmit one or more stimulation parametersconfigured to define electrical stimulation representative of thenoise-reduced signals to stimulation subsystem 104.

Stimulation subsystem 104 may be configured to generate and applyelectrical stimulation (also referred to herein as “stimulation current”and/or “stimulation pulses”) to one or more stimulation sites associatedwith an auditory pathway (e.g., the auditory nerve) of a patient inaccordance with one or more stimulation parameters transmitted theretoby sound processing subsystem 102. Exemplary stimulation sites include,but are not limited to, one or more locations within the cochlea, thecochlear nucleus, the inferior colliculus, and/or any other nuclei inthe auditory pathway. The stimulation parameters may control variousparameters of the electrical stimulation applied to a stimulation siteincluding, but not limited to, frequency, pulse width, amplitude,waveform (e.g., square or sinusoidal), electrode polarity (i.e.,anode-cathode assignment), location (i.e., which electrode pair orelectrode group receives the stimulation current), burst pattern (e.g.,burst on time and burst off time), duty cycle or burst repeat interval,spectral tilt, ramp on time, and ramp off time of the stimulationcurrent that is applied to the stimulation site.

As mentioned, the one or more stimulation sites to which electricalstimulation is applied may include any target area or location withinthe cochlea.

FIG. 2 illustrates a schematic structure of the human cochlea 200. Asshown in FIG. 2, the cochlea 200 is in the shape of a spiral beginningat a base 202 and ending at an apex 204. Within the cochlea 200 residesauditory nerve tissue 206, which is denoted by Xs in FIG. 2. Theauditory nerve tissue 206 is organized within the cochlea 200 in atonotopic manner. Low frequencies are encoded at the apex 204 of thecochlea 200 while high frequencies are encoded at the base 202. Hence,each location along the length of the cochlea 200 corresponds to adifferent perceived frequency. Stimulation subsystem 104 may thereforebe configured to apply electrical stimulation to different locationswithin the cochlea 200 (e.g., different locations along the auditorynerve tissue 206) to provide a sensation of hearing.

Returning to FIG. 1, sound processing subsystem 102 and stimulationsubsystem 104 may be configured to operate in accordance with one ormore control parameters. These control parameters may be configured tospecify one or more stimulation parameters, operating parameters, and/orany other parameter as may serve a particular application. Exemplarycontrol parameters include, but are not limited to, most comfortablecurrent levels (“M levels”), threshold current levels (“T levels”),dynamic range parameters, channel acoustic gain parameters, front andbackend dynamic range parameters, current steering parameters, amplitudevalues, pulse rate values, pulse width values, polarity values, filtercharacteristics, and/or any other control parameter as may serve aparticular application. In some examples, sound processing subsystem 102may be configured to adjust one or more of these control parameters tofacilitate the methods and systems described herein.

Auditory prosthesis system 100, including sound processing subsystem 102and stimulation subsystem 104, may include any hardware,computer-implemented instructions (e.g., software), firmware, orcombinations thereof configured to perform one or more of the processesdescribed herein. For example, auditory prosthesis system 100, includingsound processing subsystem 102 and stimulation subsystem 104, mayinclude hardware (e.g., one or more signal processors and/or othercomputing devices) configured to perform one or more of the processesdescribed herein.

One or more of the processes described herein may be implemented atleast in part as instructions executable by one or more computingdevices. In general, a processor receives instructions from acomputer-readable medium (e.g., a memory, etc.) and executes thoseinstructions, thereby performing one or more processes, including one ormore of the processes described herein. Such instructions may be storedand/or transmitted using any of a variety of known computer-readablemedia.

A computer-readable medium (also referred to as a processor-readablemedium) includes any medium that participates in providing data (e.g.,instructions) that may be read by a computing device (e.g., by aprocessor within sound processing subsystem 102). Such a medium may takemany forms, including, but not limited to, non-volatile media and/orvolatile media. Exemplary computer-readable media that may be used inaccordance with the systems and methods described herein include, butare not limited to, random access memory (“RAM”), dynamic RAM, a PROM,an EPROM, a FLASH-EEPROM, any other memory chip or cartridge, or anyother medium from which a computing device can read.

FIG. 3 illustrates exemplary components of sound processing subsystem102. As shown in FIG. 3, sound processing subsystem 102 may include adetection facility 302, a pre-processing facility 304, a frequencyanalysis facility 306, a noise reduction facility 308, a mappingfacility 310, a communication facility 312, and a storage facility 314,which may be in communication with one another using any suitablecommunication technologies. Each of these facilities 302-314 may includeany combination of hardware, software, and/or firmware as may serve aparticular application. For example, one or more of facilities 302-314may include a computing device or processor configured to perform one ormore of the functions described herein. Facilities 302-314 will now bedescribed in more detail.

Detection facility 302 may be configured to detect or sense one or moreaudio signals and convert the detected signals to correspondingelectrical signals. To this end, detection facility 302 may include amicrophone or other transducer. In some examples, the one or more audiosignals may include speech. The one or more audio signals mayadditionally or alternatively include music, noise, and/or other sounds.

Pre-processing facility 304 may be configured to perform various signalprocessing operations on the one or more audio signals detected bydetection facility 302. For example, pre-processing facility 304 mayamplify a detected audio signal, convert the audio signal to a digitalsignal, filter the digital signal with a pre-emphasis filter, subjectthe digital signal to automatic gain control, and/or perform one or moreother signal processing operations on the detected audio signal.

Frequency analysis facility 306 may be configured to divide the audiosignal into a plurality of analysis channels each containing a signalrepresentative of a distinct frequency portion of the audio signal. Forexample, frequency analysis facility 306 may include a plurality ofband-pass filters configured to divide the audio signal into a pluralityof frequency channels or bands. Additionally or alternatively, frequencyanalysis facility 306 may be configured to convert the audio signal froma time domain into a frequency domain and then divide the resultingfrequency bins into the plurality of analysis channels. To this end,frequency analysis facility 206 may include one or more componentsconfigured to apply a Discrete Fourier Transform (e.g., a Fast FourierTransform (“FFT”)) to the audio signal.

Noise reduction facility 308 may be configured to determine an overallnoise level of the signals within the analysis channels and dynamicallyadjust an amount of noise reduction applied to the signals within theanalysis channels in accordance with the determined overall noise level.For example, noise reduction facility 308 may minimize the amount ofnoise reduction applied to the signals within the analysis channels ifthe overall noise level is less than a predetermined minimum threshold,progressively increase the amount of noise reduction applied to thesignals in response to a progressive increase in the overall noise levelabove the predetermined minimum threshold, and maintain a maximum amountof noise reduction applied to the signals within the analysis channelsif the overall noise level is above a predetermined maximum threshold.Exemplary noise reduction heuristics that may be used in accordance withthe systems and methods described herein will be described in moredetail below.

Mapping facility 310 may be configured to map the noise reduced signalswithin the analysis channels to electrical stimulation pulses to beapplied to a patient via one or more stimulation channels. For example,signal levels of the noise reduced signals within the analysis channelsare mapped to amplitude values used to define electrical stimulationpulses that are applied to the patient by stimulation subsystem 104 viaone or more corresponding stimulation channels. Mapping facility 310 maybe further configured to perform additional processing of the signalscontained within the analysis channels, such as signal compression.

Communication facility 312 may be configured to facilitate communicationbetween sound processing subsystem 102 and stimulation subsystem 104.For example, communication facility 312 may include one or more coilsconfigured to transmit control signals and/or power via one or morecommunication links to stimulation subsystem 104. Additionally oralternatively, communication facility 312 may one or more wires or thelike that are configured to facilitate direct communication withstimulation subsystem 104.

Storage facility 314 may be configured to maintain audio signal data 316representative of an audio signal detected by detection facility 302 andcontrol parameter data 318 representative of one or more controlparameters, which may include one or more stimulation parameters to betransmitted from sound processing subsystem 102 to stimulation subsystem104. Storage facility 314 may be configured to maintain additional oralternative data as may serve a particular application.

FIG. 4 illustrates exemplary components of stimulation subsystem 104. Asshown in FIG. 4, stimulation subsystem 104 may include a communicationfacility 402, a current generation facility 404, a stimulation facility406, and a storage facility 408, which may be in communication with oneanother using any suitable communication technologies. Each of thesefacilities 402-408 may include any combination of hardware, software,and/or firmware as may serve a particular application. For example, oneor more of facilities 402-408 may include a computing device orprocessor configured to perform one or more of the functions describedherein. Facilities 402-408 will now be described in more detail.

Communication facility 402 may be configured to facilitate communicationbetween stimulation subsystem 104 and sound processing subsystem 102.For example, communication facility 402 may include one or more coilsconfigured to receive control signals and/or power via one or morecommunication links to stimulation subsystem 104. Communication facility402 may additionally or alternatively be configured to transmit one ormore status signals and/or other data to sound processing subsystem 102.

Current generation facility 404 may be configured to generate electricalstimulation in accordance with one or more stimulation parametersreceived from sound processing subsystem 102. To this end, currentgeneration facility 404 may include one or more current generatorsand/or any other circuitry configured to facilitate generation ofelectrical stimulation.

Stimulation facility 406 may be configured to apply the electricalstimulation generated by current generation facility 404 to one or morestimulation sites within the cochlea of a patient. To this end, as willbe illustrated in more detail below, stimulation facility 406 mayinclude one or more electrodes disposed on a lead that may be insertedwithin the cochlea, into one or more nuclei in the auditory pathway(e.g., into the cochlear nucleus and/or the inferior colliculus), and/orat any other location along the auditory pathway.

Storage facility 408 may be configured to maintain stimulation parameterdata 410 as received from sound processing subsystem 102. Stimulationparameter data 410 may be representative of one or more stimulationparameters configured to define the electrical stimulation generated andapplied by stimulation subsystem 104. Storage facility 408 may beconfigured to maintain additional or alternative data as may serve aparticular application.

FIG. 5 illustrates an exemplary cochlear implant system 500, which mayimplement auditory prosthesis system 100. It will be recognized thatcochlear implant system 500 is one of many different types of systemsthat may implement auditory prosthesis system 100. For example, in somealternative implementations, a brainstem implant and/or any other typeof auditory prosthesis may be implanted within a patient and configuredto apply stimulation to one or more stimulation sites located along anauditory pathway of a patient.

As shown in FIG. 5, cochlear implant system 500 may include a microphone502, a sound processor 504, a headpiece 506 having a coil 508 disposedtherein, an implantable cochlear stimulator (“ICS”) 510, a lead 512, anda plurality of electrodes 514 disposed on the lead 512. Additional oralternative components may be included within cochlear implant system500 as may serve a particular application. The facilities describedherein may be implemented by or within one or more components shownwithin FIG. 5. For example, detection facility 302 may be implemented bymicrophone 502. Pre-processing facility 304, frequency analysis facility306, noise reduction facility 308, mapping facility 310, and/or storagefacility 314 may be implemented by sound processor 504. Communicationfacility 312 may be implemented by headpiece 506 and coil 508.Communication facility 402, current generation facility 404, and storagefacility 408 may be implemented by implantable cochlear stimulator 508.Stimulation facility 406 may be implemented by lead 510 and electrodes512.

As shown in FIG. 5, microphone 502, sound processor 504, and headpiece506 may be located external to a patient. In some alternative examples,microphone 502 and/or sound processor 504 may be implanted within thepatient. In such configurations, the need for headpiece 506 may beobviated.

Microphone 502 may detect an audio signal and convert the detectedsignal to a corresponding electrical signal. Microphone 502 may beplaced external to the patient, within the ear canal of the patient, orat any other suitable location as may serve a particular application.The electrical signal may be sent from microphone 502 to sound processor504 via a communication link 514, which may include a telemetry link, awire, and/or any other suitable communication link.

Sound processor 504 is configured to process the converted audio signalin accordance with a selected sound processing strategy to generateappropriate stimulation parameters for controlling implantable cochlearstimulator 510. Sound processor 504 may include or be implemented withina behind-the-ear (“BTE”) unit, a portable speech processor (“PSP”),and/or any other sound processing unit as may serve a particularapplication. Exemplary components of sound processor 504 will bedescribed in more detail below.

Sound processor 504 may be configured to transcutaneously transmit data(e.g., data representative of one or more stimulation parameters) toimplantable cochlear stimulator 504 via coil 508. As shown in FIG. 5,coil 508 may be housed within headpiece 506, which may be affixed to apatient's head and positioned such that coil 508 is communicativelycoupled to a corresponding coil (not shown) included within implantablecochlear stimulator 510. In this manner, data may be wirelesslytransmitted between sound processor 504 and implantable cochlearstimulator 510 via communication link 518. It will be understood thatdata communication link 118 may include a bi-directional communicationlink and/or one or more dedicated uni-directional communication links.In some alternative embodiments, sound processor 504 and implantablecochlear stimulator 510 may be directly connected with one or more wiresor the like.

Implantable cochlear stimulator 510 may be configured to generateelectrical stimulation representative of an audio signal detected bymicrophone 502 in accordance with one or more stimulation parameterstransmitted thereto by sound processing subsystem 102. Implantablecochlear stimulator 510 may be further configured to apply theelectrical stimulation to one or stimulation sites within the cochleavia one or more electrodes 514 disposed along lead 512.

To facilitate application of the electrical stimulation generated byimplantable cochlear stimulator 510, lead 512 may be inserted within aduct of the cochlea such that electrodes 514 are in communication withone or more stimulation sites within the cochlea. As used herein, theterm “in communication with” refers to electrodes 514 being adjacent to,in the general vicinity of, in close proximity to, directly next to, ordirectly on the stimulation site. Any number of electrodes 514 (e.g.,sixteen) may be disposed on lead 512 as may serve a particularapplication.

FIG. 6 illustrates components of an exemplary sound processor 504coupled to an implantable cochlear stimulator 510. The components shownin FIG. 6 may be configured to perform one or more of the processesassociated with one or more of the facilities 302-314 associated withsound processing subsystem 102 and are merely representative of the manydifferent components that may be included within sound processor 504.

As shown in FIG. 6, microphone 502 senses an audio signal, such asspeech or music, and converts the audio signal into one or moreelectrical signals. These signals are then amplified in audio front-end(“AFE”) circuitry 602. The amplified audio signal is then converted to adigital signal by an analog-to-digital (“A/D”) converter 604. Theresulting digital signal is then subjected to automatic gain controlusing a suitable automatic gain control (“AGC”) unit 606.

After appropriate automatic gain control, the digital signal issubjected to a plurality of filters 610 (e.g., a plurality of band-passfilters). Filters 610 are configured to divide the digital signal into manalysis channels 608 each containing a signal representative of adistinct frequency portion of the audio signal sensed by microphone 502.Additional or alternative components may be used to divide the signalinto the analysis channels 608 as may serve a particular application.For example, as described previously, one or more components may beincluded within sound processor 504 that are configured to apply aDiscrete Fourier Transform to the audio signal and then divide theresulting frequency bins into the analysis channels 608.

As shown in FIG. 6, the signals within each analysis channel 608 may beinput into an energy detector 612. Each energy detector 612 may includeany combination of circuitry configured to detect an amount of energycontained within each of the signals within the analysis channels 608.For example, each energy detector 612 may include a rectificationcircuit followed by an integrator circuit.

After energy detection, the signals within the m analysis channels 608are input into a noise reduction module 614. Noise reduction module 614may perform one or more of the functions described in connection withnoise reduction facility 308. For example, noise reduction module 614may determine an overall noise level of the signals within the analysischannels and dynamically adjust an amount of noise reduction applied tothe signals within the analysis channels in accordance with thedetermined overall noise level. Noise reduction module 614 will bedescribed in more detail below.

Mapping module 616 may perform one or more of the functions described inconnection with mapping facility 310. For example, mapping module 616may map the signals in the analysis channels 608 to one or morestimulation channels after the signals have been subjected to noisereduction by noise reduction module 614. For example, signal levels ofthe noise reduced signals included within the m analysis channels 608are mapped to amplitude values used to define the electrical stimulationpulses that are applied to the patient by implantable cochlearstimulator 510 via M stimulation channels 620. In some examples, groupsof one or more electrodes 514 may make up the M stimulation channels620.

The mapped signals may be serialized by a multiplexer 618 andtransmitted to implantable cochlear stimulator 510. The implantablecochlear stimulator 510 may then apply electrical stimulation via one ormore of the M stimulation channels 620 to one or more stimulation siteswithin the duct of the patient's cochlea.

FIG. 7 illustrates an exemplary dynamic noise reduction method 700 thatmay be used in an auditory prosthesis system. While FIG. 7 illustratesexemplary steps according to one embodiment, other embodiments may omit,add to, reorder, and/or modify any of the steps shown in FIG. 7. It willbe recognized that any of the systems, subsystems, facilities, and/ormodules may be configured to perform one or more of the steps shown inFIG. 7.

In step 702, an audio signal presented to an auditory prosthesis patientis divided into a plurality of analysis channels each containing asignal representative of a distinct frequency portion of the audiosignal. Step 702 may be performed by frequency analysis facility 306,for example, in any of the ways described herein.

In step 704, an overall noise level of the signals within the analysischannels is determined. To illustrate, FIG. 8 shows exemplary componentsthat may be included within noise reduction module 614 that may be usedto determine the overall noise level of the signals within analysischannels 608 shown in FIG. 6. As shown in FIG. 8, noise reduction module614 may include an energy estimator 802, a noise estimator 804, a gainmodule 806, a summation block 808, and an overall noise level estimator810 communicatively coupled to one another.

Energy estimator 802, noise estimator 804, gain module 806, andsummation block 808 are included within dashed lines 812 to illustratethat they are specific to a particular analysis channel 608. Hence, insome examples, each of these components 802-808 may be replicated foreach analysis channel 608. In some examples, a single component (e.g., adigital signal processor) or combination of components may be configuredto perform the functions associated with each of the components 802-808for each of the signals contained within analysis channels 608.

As shown in FIG. 8, energy estimator 802 may be configured to estimateor otherwise determine an energy level of a signal contained within aparticular analysis channel 608. The energy level may be estimated inany suitable manner as may serve a particular application. The energylevel of the signal contained within analysis channel 608 may berepresented as S[m,t], where m represents the particular analysischannel number and t represents time. Hence, S[m,t] represents theenergy level estimate of the signal in channel m at time t.

The estimated energy level is input into noise estimator 804, whichanalyzes the estimated energy level to determine an estimated noiselevel of the signal. The estimated noise level may be determined in anysuitable manner as may serve a particular application and may berepresented as N[m,t], where m represents the particular analysischannel number and t represents time. Hence, N[m,t] represents the noiselevel estimate in channel m at time t. For example, N[m,t] may beestimated by detecting stationary steady components in the signalS[m,t]. Alternatively, noise may be estimating by measuring signalS[m,t] during absence of speech, as cued by a voice activity detectorcircuit.

Gain module 806 may be configured to accept both S[m,t] and N[m,t] andtake the ratio thereof to determine a signal-to-noise ratio (“SNR”) ofthe signal contained within analysis channel 608, which may berepresented by SNR[m,t]. As will be described in more detail below, gainmodule 806 may use SNR[m,t] in combination with an overall noise levelvalue as determined by overall noise level estimator 810 to determine anappropriate gain to be applied to the signal contained within analysischannel 608. In some examples, the gain is applied to the signal viasummation block 808.

As shown in FIG. 8, N[m,t] may also be input into overall noise levelestimator 810. Overall noise level estimator 810 may additionallyreceive noise level estimates of each of the other analysis channels andcompute the overall noise level of the signals contained within theanalysis channels in accordance with Equation 1:

$\begin{matrix}{{N\lbrack t\rbrack} = \sqrt{\sum\limits_{m}\; {N\left\lbrack {m,t} \right\rbrack}^{2}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

Overall noise level estimator 810 may be further configured to integrateN[t] over time in accordance with Equation 2:

Ns[t]=α*Ns[t−1]+(1−α)*Ns[t]  (Equation 2)

Returning to FIG. 7, in step 706, an amount of noise reduction appliedto the signals within the analysis channels is dynamically adjusted inaccordance with the overall noise level as determined in step 704. Theamount of noise reduction applied to the signals within the analysischannels may be dynamically adjusted by adjusting an amount of gainapplied to the signals with gain module 806. For example, gain module806 may be configured to adjust an amount of gain applied to the signalin accordance with the overall noise level of the signals withinanalysis channels 608. The amount of gain may be adjusted in anysuitable manner as may serve a particular application. For example, gainmodule 806 may be configured to compute the gain per analysis channelaccording to Equation 3:

G[m,t]=G(SNR[m,t])^(C(Ns[t]))  (Equation 3)

In Equation 3, G(SNR[m,t]) represents the gain determined by gain module806 without the additional input of N[t]. C(Ns[t]) represents acorrection to the gain determination that is based on the overall noiselevel of the signals contained within the analysis channels 608.C(Ns[t]) is typically equal to zero below a predetermined minimumthreshold (e.g., 25 dB SPL). In such instances, G[m,t] is always equalto one. In other words, noise reduction is minimized when C(Ns[t]) isequal to zero.

C(Ns[t]) is typically equal to one above a predetermined maximumthreshold (e.g., 40 dB SPL). In such instances, full gain (i.e., maximumnoise reduction) is applied to the signals contained within the analysischannels 608. In between the predetermined minimum and maximum thresholdlevels, C(Ns[t]) may be linear function of Ns[t].

In this manner, the amount of noise reduction applied to the signalscontained within analysis channels 608 may be minimized if the overallnoise level N[t] is less than the predetermined minimum threshold,progressively increased in response to a progressive increase in theoverall noise level N[t] above the predetermined minimum threshold, andmaintained at a maximum amount if the overall noise level N[t] is abovea predetermined maximum threshold. Hence, in quiet environments wherethe overall noise level N[t] is less than the predetermined minimumthreshold, noise reduction module 614 may cease applying noise reductionto detected audio signals or otherwise minimize the amount of noisereduction applied to detected audio signals so that the patient canperceive environmental sounds.

Additionally or alternatively, noise reduction module 614 may beconfigured to dynamically adjust an amount of noise reduction applied tothe signals within analysis channels 608 by adjusting one or moreparameters used by mapping module 616 to map the signals to electricalstimulation pulses to be applied to a patient via one or morestimulation channels 620.

To illustrate, FIG. 9 shows a curve 902 (shown with diamonds disposedthereon for illustrative purposes) that represents an exemplary mappingfunction that may be used by mapping module 616 in the absence of noisereduction to map loudness levels of the signals contained withinanalysis channels 608 to amplitudes of stimulation pulses used torepresent the signals when applied to a patient. The mapping functionmay be defined by a T level, an M level, and a dynamic range (alsoreferred to herein as an “input dynamic range” or “IDR”). The T levelrepresents a minimum amplitude of stimulation current which when appliedto a given electrode associated with the channel produces a sensedperception of sound. The M level represents a most comfortable amplitudeof stimulation current which when applied to the given electrodeproduces a sensed perception of sound that is moderately loud, orcomfortably loud, but not so loud that the perceived sound isuncomfortable. The sound amplitude associated with M level stimulationis set to a suitable value (e.g., 55 dB SPL). The sound amplitudeassociated with T level stimulation is equal to the sound amplitudeassociated with M level stimulation minus the IDR. In other words, IDRrepresents the difference (in SPL) between sound amplitude producing Tlevel stimulation and sound amplitude producing M level stimulation.

The T and M levels are specific to a particular patient. For example, aT level associated with a particular patient may be equal to 200microamps and a M level associated with the particular patient may beequal to 1000 microamps. As shown in FIG. 9, The T level may be mappedto any suitable loudness level (e.g., 20 dB SPL). Likewise, the M levelmay be mapped to any suitable loudness level (e.g., 60 dB SPL).

FIG. 10 shows another curve 1002 (shown with squares disposed thereonfor illustrative purposes) that illustrates an effect on the mappingfunction associated with curve 902 of applying 10 dB of attenuation toall signal levels. The mapping function illustrated by curve 1002corresponds to a configuration where noise reduction is applieduniformly to all loudness levels as opposed to being dynamicallyadjusted depending on the particular noise level. As shown in FIG. 10,curve 1002 is uniformly shifted down. Such a shift may result in somelow level signals being attenuated below the patient's T level (e.g., 20dB SPL), thus resulting in the patient not being able to perceive soundsat these levels.

In some examples, noise reduction module 614 may be configured todynamically adjust an amount of noise reduction applied to the signalswithin analysis channels 608 by increasing the T level of a patient tomatch the predetermined minimum threshold below which noise reduction isminimized. Additionally or alternatively, noise reduction module 614 maybe configured to dynamically adjust an amount of noise reduction appliedto the signals within analysis channels 608 by increasing the dynamicrange.

For example, FIG. 11 shows another curve 1102 (shown with trianglesdisposed thereon for illustrative purposes) representative of a mappingfunction using noise reduction described in connection with FIG. 10after the dynamic range has been increased by 10 dB. As shown in FIG.11, the increase in dynamic range effectively decreases the slope ofcurve 1102, thereby preventing relatively lower level signals from beingattenuated and at the same time allowing relatively higher level signalsto be attenuated. An increase in the T level may similarly decrease theslope of curve 1102.

As a further illustration, suppose that a particular mapping functionhas a M level corresponding to 60 dB SPL and a T level corresponding to60−IDR. In between these two values, the mapping may be linear. Thus,for any level A, the mapping function may be represented by MAP(A),which may be equal to (M−T)/IDR*(A−60+1DR)+T. Suppose that A is theambiance level in a quiet room (e.g. 25 dB SPL). To derive a new mappingfunction MAPnew(A), where MAP(A)=MAPnew(A−Nr), T may be changed in thenew function as follows: Tnew=M*Nr/(Nr+Ad)+T*Ad/(Nr+Ad). In thisequation, Ad=60−A and Nr is the amount in dB by which ambient noise isattenuated by noise reduction.

In some examples, the predetermined minimum threshold below which noisereduction is minimized may set to substantially equal a T level of aparticular patient. Likewise, the predetermined maximum threshold abovewhich a maximum amount of noise reduction is maintained may be set tosubstantially equal a M level of a particular patient. It will berecognized that the predetermined minimum and maximum thresholds may beset to equal any value as may serve a particular application and thatthey may vary from patient to patient.

In some examples, the T level of a particular patient may beautomatically and/or manually adjusted during a fitting session. Forexample, a clinician may present a variety of environmental sounds to apatient during a fitting session and adjust a T level parameterassociated with the patient until the thresholds are audible to thepatient.

In some examples, the release of noise reduction is coordinated with theaction of the AGC unit 606. In this manner, the effect on patientperception of dynamic application of noise reduction may be minimized.For example, an amount of noise reduction applied to signals withinanalysis channels may be decreased during a time frame associated with arelease of gain of the AGC unit 606.

FIG. 12 illustrates another exemplary dynamic noise reduction method1200 that may be used in an auditory prosthesis system. While FIG. 12illustrates exemplary steps according to one embodiment, otherembodiments may omit, add to, reorder, and/or modify any of the stepsshown in FIG. 12. It will be recognized that any of the systems,subsystems, facilities, and/or modules may be configured to perform oneor more of the steps shown in FIG. 12.

In step 1202, an audio signal presented to an auditory prosthesispatient is divided into a plurality of analysis channels each containinga signal representative of a distinct frequency portion of the audiosignal. Step 1202 may be performed by frequency analysis facility 306,for example, in any of the ways described herein.

In step 1204, an overall noise level of the signals within the analysischannels is determined. The overall noise level may be determined in anyof the ways described herein.

In step 1206, an amount of noise reduction applied to the signals withinthe analysis channels is minimized if the overall noise level is lessthan a predetermined minimum threshold. The amount of noise reductionmay be minimized in any of the ways described herein.

In step 1208, the amount of noise reduction applied to the signalswithin the analysis channels is progressively increased in response to aprogressive increase in the overall noise level above the predeterminedminimum threshold. The noise reduction may be progressively increased inany of the ways described herein.

As detailed above, the methods and systems described herein facilitatedynamic noise reduction in auditory prosthesis systems. As an example,an exemplary method includes dividing an audio signal presented to anauditory prosthesis patient into a plurality of analysis channels eachcontaining a signal representative of a distinct frequency portion ofthe audio signal, determining an overall noise level of the signalswithin the analysis channels, and dynamically adjusting an amount ofnoise reduction applied to the signals within the analysis channels inaccordance with the determined overall noise level. The dynamicadjustment of noise reduction is configured to minimize the amount ofnoise reduction applied to the signals within the analysis channels ifthe overall noise level is less than a predetermined minimum threshold.

Another exemplary method includes dividing an audio signal presented toan auditory prosthesis patient into a plurality of analysis channelseach containing a signal representative of a distinct frequency portionof the audio signal, determining an overall noise level of the signalswithin the analysis channels, minimizing an amount of noise reductionapplied to the signals within the analysis channels if the overall noiselevel is less than a predetermined minimum threshold, and progressivelyincreasing the amount of noise reduction applied to the signals withinthe analysis channels in response to a progressive increase in theoverall noise level above the predetermined minimum threshold.

An exemplary system includes a frequency analysis facility configured todivide an audio signal into a plurality of analysis channels eachcontaining a signal representative of a distinct frequency portion ofthe audio signal and a noise reduction facility communicatively coupledto the channel facility. The noise reduction facility is configured todetermine an overall noise level of the signals within the analysischannel and dynamically adjust an amount of noise reduction applied tothe signals within the analysis channels in accordance with thedetermined overall noise level. The dynamic adjustment of noisereduction is configured to minimize the amount of noise reductionapplied to the signals within the analysis channels if the overall noiselevel is less than a predetermined minimum threshold.

In some examples, the sound amplitude of an audio signal that is above anoise floor (e.g., the predetermined minimum threshold) may bedynamically increased to compensate for the loss of amplitude thatoccurs as a result of the noise reduction described herein. The soundamplitude may be dynamically increased in any suitable manner as mayserve a particular implementation.

In the preceding description, various exemplary embodiments have beendescribed with reference to the accompanying drawings. It will, however,be evident that various modifications and changes may be made thereto,and additional embodiments may be implemented, without departing fromthe scope of the invention as set forth in the claims that follow. Forexample, certain features of one embodiment described herein may becombined with or substituted for features of another embodimentdescribed herein. The description and drawings are accordingly to beregarded in an illustrative rather than a restrictive sense.

1. A method comprising: dividing, by a sound processing subsystem, anaudio signal presented to an auditory prosthesis patient into aplurality of analysis channels each containing a signal representativeof a distinct frequency portion of the audio signal; determining, by thesound processing subsystem, an overall noise level of the signals withinthe analysis channels; and dynamically adjusting, by the soundprocessing subsystem, an amount of noise reduction applied to thesignals within the analysis channels in accordance with the determinedoverall noise level, the dynamically adjusting configured to minimizethe amount of noise reduction applied to the signals within the analysischannels if the overall noise level is less than a predetermined minimumthreshold.
 2. The method of claim 1, wherein the dynamically adjustingis further configured to progressively increase the amount of noisereduction applied to the signals within the analysis channels inresponse to a progressive increase in the overall noise level above thepredetermined minimum threshold.
 3. The method of claim 2, wherein theprogressive increase in the amount of noise reduction applied to thesignals within the analysis channels is linear.
 4. The method of claim1, wherein the dynamically adjusting is further configured to maintain amaximum amount of noise reduction applied to the signals within theanalysis channels if the overall noise level is above a predeterminedmaximum threshold.
 5. The method of claim 4, wherein the predeterminedmaximum threshold is substantially equal to a most comfortable currentlevel associated with the patient.
 6. The method of claim 1, wherein thedynamically adjusting comprises automatically or manually increasing a Tlevel parameter used to map a loudness level of the signals within theanalysis channels to an amplitude of electrical stimulation applied by astimulation subsystem to the patient.
 7. The method of claim 1, whereinthe dynamically adjusting comprises increasing a dynamic range parameterused to map a loudness level of the signals within the analysis channelsto an amplitude of electrical stimulation applied by a stimulationsubsystem to the patient.
 8. The method of claim 1, further comprisingdynamically increasing, by the sound processing subsystem, a soundamplitude of the audio signal if the audio signal has an amplitude abovethe predetermined minimum threshold.
 9. The method of claim 1, furthercomprising decreasing, by the sound processing subsystem, the amount ofnoise reduction applied to the signals within the analysis channelsduring a time frame associated with a release of gain of an automaticgain control unit.
 10. A method comprising: dividing, by a soundprocessing subsystem, an audio signal presented to an auditoryprosthesis patient into a plurality of analysis channels each containinga signal representative of a distinct frequency portion of the audiosignal; determining, by the sound processing subsystem, an overall noiselevel of the signals within the analysis channels; minimizing, by thesound processing subsystem, an amount of noise reduction applied to thesignals within the analysis channels if the overall noise level is lessthan a predetermined minimum threshold; and progressively increasing, bythe sound processing subsystem, the amount of noise reduction applied tothe signals within the analysis channels in response to a progressiveincrease in the overall noise level above the predetermined minimumthreshold.
 11. The method of claim 10, further comprising maintaining,by the sound processing subsystem, a maximum amount of noise reductionapplied to the signals within the analysis channels if the overall noiselevel is above a predetermined maximum threshold.
 12. The method ofclaim 10, further comprising increasing, by the sound processingsubsystem, a T level parameter used to map a loudness level of thesignals within the analysis channels to an amplitude of electricalstimulation applied by a stimulation subsystem to the patient.
 13. Themethod of claim 10, further comprising increasing, by the soundprocessing subsystem, a dynamic range parameter used to map a loudnesslevel of the signals within the analysis channels to an amplitude ofelectrical stimulation applied by a stimulation subsystem to thepatient.
 14. The method of claim 10, further comprising decreasing, bythe sound processing subsystem, the amount of noise reduction applied tothe signals within the analysis channels during a time frame associatedwith a release of gain of an automatic gain control unit.
 15. A systemcomprising: a frequency analysis facility configured to divide an audiosignal into a plurality of analysis channels each containing a signalrepresentative of a distinct frequency portion of the audio signal; anda noise reduction facility communicatively coupled to the channelfacility and configured to determine an overall noise level of thesignals within the analysis channel, and dynamically adjust an amount ofnoise reduction applied to the signals within the analysis channels inaccordance with the determined overall noise level, the dynamicadjustment configured to minimize the amount of noise reduction appliedto the signals within the analysis channels if the overall noise levelis less than a predetermined minimum threshold.
 16. The system of claim15, wherein the dynamic adjustment is further configured toprogressively increase the amount of noise reduction applied to thesignals within the analysis channels in response to a progressiveincrease in the overall noise level above the predetermined minimumthreshold.
 17. The system of claim 15, wherein the noise reductionfacility is further configured to dynamically adjust the amount of noisereduction applied to the signals by increasing a T level parameter usedto map a loudness level of the signals within the analysis channels toan amplitude of electrical stimulation applied by an auditory prosthesisto the patient.
 18. The system of claim 15, wherein the noise reductionfacility is further configured to dynamically adjust the amount of noisereduction applied to the signals by increasing a dynamic range parameterused to map a loudness level of the signals within the analysis channelsto an amplitude of electrical stimulation applied by an auditoryprosthesis to the patient.
 19. The system of claim 15, furthercomprising an implantable cochlear stimulator configured to applyelectrical stimulation representative of the audio signal to thepatient.
 20. The system of claim 15, wherein the frequency analysisfacility and the noise reduction facility are implemented within a soundprocessor.